Several production processes have been conventionally known for the cyanobenzaldehyde compounds, cyanobenzoyl halide compounds and cyanobenzoic acid compounds.
First, a production process for p-cyano-benzaldehyde, a representative example of cyanobenzaldehyde compounds, will be described.
(1) The p-cyanobenzaldehyde is classically synthesized by converting p-cyanobenzoic acid into p-cyanobenzoyl chloride with a chlorinating agent such as thionyl chloride and subjecting the p-cyanobenzoyl chloride to Rosenmund reduction [see, Rapopport et al., J. Am. chem. Soc., 75 (1953), 1125].
(2) A method of reacting p-bromomethylbenzonitrile with hexamethylenetetramine in chloroform and subjecting the salt | Eli precipitated to thermal decomposition with an acetic acid-water solvent is also known [see, Dyer et al., J. Chem. Soc., (1952) 4778].
(3) As a modification of (2), a method of reacting p-chloromethylbenzonitrile with hexamethylenetetramine in an oil-water two-layer system is known (see, JP-A-60-166655 (the term "JP-A" as used herein means an "unexamined published Japanese patent application)).
Further, (4) electrolytical oxidization methods of cyanobenzylamines such as a method of electrolytically oxidizing p-cyanobenzylamine in the presence of 2,6-lutidine and a perchlorate using 2,2,6,6-tetramethylplperidinyl-1-oxide as a mediator are also known [see, Semmelhack et al., J. Am. Chem. Soc., 105 (1983) 6732].
Furthermore, (5) a method of oxidizing p-cyano-N,N-dimethylbenzylamine with iodosylbenzene in the presence of a catalytic amount of iron-porphyrin complex (Smith et al., J. Chem. Soc. Chem. Commun., 64 (1985)).
These synthesis methods of p-cyanobenzaldehyde each has a problem.
In the Rosenmund reduction method in (1) above, this starting compound requires multiple stages for the synthesis thereof and is low in yield.
In the method of using p-halogenomethylbenzonitrile as a starting material in (2) and (3) above, p-tolunitrile as a raw material is difficult to procure and moreover, since hexamethylenetetramine in excess of the stoichiometric amount is required, a large amount of wastes is produced and this causes environmental problems.
Further, in the electrolytic oxidation of p-cyanobenzylamine in (4) above, an 8-fold amount of tertiary amine is necessary, a 20% molar amount of oxidation mediator is required and moreover, the oxidation mediator decomposes as the reaction proceeds, thus, this method is not suitable for the production in large quantities at a low cost.
Further, the oxidation of p-cyano-N,N-dimethylbenzylamine in (5) above, a stoichiometric amount of an oxidizing agent is used and a porphyrin complex catalyst which is expensive and tends to decompose is necessary, so that it is uneconomical.
As described in the foregoing, conventionally known techniques for producing p-cyanobenzaldehyde are disadvantageous in that the synthesis is cumbersome, a high-purity entity is difficult to obtain, and the raw material is not easily procured.
Furthermore, as the method of producing cyanobenzoyl halide compound, a method of reacting a corresponding cyanobenzoic acid compound with an acid halogenating agent has been proposed. As a representative example, a method of reacting p-cyanobenzoic acid with an acid chlorinating agent to obtain p-cyanobenzoyl chloride is recited.
There have been proposed (6) a method of using thionyl chloride as the acid chlorinating agent (JP-B-1-31501(the term "JP-B" as used herein means an "examined published Japanese patent application)), (7) a method of using oxalyl chloride (Robert J. Weikert, et al., J. Med. Chem., 3, 1630 (1991)) and (8) a method of using phosphorus pentachloride (Raffaello Fusco, et al., Ann. Chim (Rome), 42, 94 (1952)).
These methods have the following problems and hence they are not always advantageous for practice on an industrial scale.
That is, the method of using thionyl chloride in (6) above by-produces sulfur dioxide, which is a cause of air pollution and has the problem that separation and detoxification treatment of sulfur dioxide is costly.
The method of using oxalyl chloride in (7) above by-produces carbon monoxide, which is also a cause of air pollution and it has a problem that its detoxification treatment is costly.
Furthermore, the method of using phosphorus pentachloride in (8) above produces a by-product containing phosphorus compounds. Since it serves as a source of enrichment material for lakes and rivers and is a cause of environmental pollution, the phosphorus-containing byproduct has to be discarded after suitable treatment thereof.
As described above, the conventionally known production methods for cyanobenzoyl halide compounds have the problems that they involve a difficulty in separation and detoxification treatment of by-products and after the reaction, the treatment for reducing loads on environment upon disposal of by-products after the reaction is costly.
Further, several production methods for cyanobenzoic acid compounds are known. As a representative example, a production method for p-cyanobenzoic acid is cited.
p-Cyanobenzoic acid has classically been synthesized by (9) Sandmeyer reaction in which p-aminobenzoic acid is diazotized and reacted with copper cyanide (Lucas et al., J. Am. Chem. Soc., 51 (1929) 2718).
Furthermore, (10) a synthesis method of oxidizing tolunitrile with a strong oxidizing agent such as chromic acid or permanganic acid is also known (Levine et al., J. Org. Chem., 24, 115 (1959), Kattwinkel et al., Chem. Ber., 37, 3226 (1904)).
More recently, (11) it has been known that p-cyanobenzoic acid can be synthesized by carbonylating 4-chlorocyanobenzene using a palladium-phosphine catalyst in the presence of carbon monoxide (JP-A-64-47).
As related art to the present invention, (12) a method of oxidizing p-tolunitrile with sodium hypochlorite as an oxidizing agent using a ruthenium compound as an oxidizing catalyst in a two-layer system consisting of water and an organic solvent in the presence of a phase transfer catalyst (Yoel et al., J. Org. Chem., 51, 2880 (1986)). In the literature, tolunitrile has been reported to be converted to p-cyanobenzoic acid via p-cyanobenzaldehyde.
Furthermore, (13) as a method of oxidizing p-cyanobenzaldehyde, a method of using a cobalt catalyst in an oxygen atmosphere in the presence of acetic anhydride and n-butyraldehyde (Punniyamurthy et al., Tetrahedron Letters., 35, 2959 (1994)) and a method of using sodium perborate in acetic acid solvent (Norich et al., Tetrahedron, 45, 3299 (1989)) have been known.
However, these conventional production methods for cyanobenzoic acid have several problems.
The Sandmeyer method in (9) above needs dangerous copper cyanide and isolation and purification of p-cyanobenzoic acid is difficult under acidic conditions where hydrogen cyanide is released.
In the case where the oxidizing agent such as chromic acid or permanganic acid in (10) above is used, toxic heavy metal wastes are produced in excess of the stoichiometric amount so that a large amount of wastes containing toxic heavy metals is generated, which causes severe problems on the environment.
The carbonylation method in (11) above uses expensive palladium and phosphine so that it is uneconomical.
Furthermore, the method of using a ruthenium compound in (12) above needs 1 mol % of an expensive ruthenium compound and 5 mol % of a phase transfer catalyst as an indispensable component to a raw material so that it is an uneconomical method.
Furthermore, of the methods for the oxidization of p-cyanobenzaldehyde in (13) above, both the oxidation method with oxygen and the method using sodium perborate are low in yield.
As described above, there have been the problems that the cyanobenzoic acid compounds are difficult to obtain in pure forms since their synthesis is complexed according to the conventionally known production methods and raw materials are difficult to obtain.